Plus, even if you manage to never, ever have a drive fail, accidentally delete something that you wanted to keep, inadvertently screw up a filesystem, crash into a corruption bug, have malware destroy stuff, make an error in writing it a script causing it to wipe data, just realize that an old version of something you overwrote was still something you wanted, or run into any of the other ways in which you could lose data…
You gain the peace of mind of knowing that your data isn’t a single point of failure away from being gone. I remember some pucker-inducing moments before I ran backups. Even aside from not losing data on a number of occasions, I could sleep a lot more comfortably on the times that weren’t those occasions.
If you’re interested in home automation, I think that there’s a reasonable argument for running it on separate hardware. Not much by way of hardware requirements, but you don’t want to take it down, especially if it’s doing things like lighting control.
Same sort of idea for some data-logging systems, like weather stations or ADS-B receivers.
Other than that, though, I’d probably avoid running an extra system just because I have hardware. More power usage, heat, and maintenance.
EDIT: Maybe hook it up to a power management device, if you don’t have that set up, so that you can power-cycle your other hardware remotely.